High power laser beam as used herein refers to a laser beam having an average power ranging from approximately one watt to hundreds of watts. High power gas and solid state lasers are used extensively in manufacturing processes today because of cost savings and product quality improvements realized through their use. Due to the high capital costs of power lasers, however, one design objective to be achieved in implementing such a laser in a manufacturing system is to maximize the utilization of the power laser. In broadest terms, this requires making the power laser generated beam available to as many manufacturing functions as possible. A second design objective synergistic with the objective of maximizing laser utilization is to maximize the manufacturing system's flexibility to deliver the laser beam to the multiple, spatially separated process points where it is required on a manufacturing workpiece. One technique known in the art for providing such flexibility is to direct the laser beam through one end of an optical fiber so that the other end of the fiber may be moved between the multiple process points on the workpiece. Apparatus for the practice of such a technique is disclosed in commonly assigned U.S. Pat. No. 4,564,736.
In view of the above described flexibility afforded by fiber optic delivery of the high power laser beam, it would be desirable to provide apparatus for splitting the power laser beam and delivering the split beam portions through different multiple optical fibers each of which terminate at a different one of the workpiece process points. Given the flexibility of delivering the full power of the high power laser beam to the workpiece via an optical fiber, it would be further desirable to provide apparatus for coupling the beam delivered by that single fiber into the multiple fibers which terminate at the different workpiece process point locations.
There are at least two major techniques known in the art for coupling together multiple optical fibers to enable the laser beam transmitted through one incoming fiber to be coupled into the remaining outgoing fibers for continued transmission through those fibers. Each of these two techniques is, however, to the extent the inventors herein are aware, limited to communication and low power applications in which the laser beam average power is substantially less than one watt. In general, design considerations and different coupling techniques for coupling fibers transmitting low power laser beams are surveyed in the paper entitled "A Review of Optical Fiber Connection Technology" by Dalgleish, Proceedings of 25th International Wire and Cable Symposium, Nov. 1976, pp. 240-246. One of the major coupling techniques consists of using a connector. In one type of connector, the respective end portions of the fibers being coupled are each rigidly supported in respective connector fittings. In such connector fittings, each fiber end is typically supported within a metal or ceramic ferrule which is in turn supported within the fitting. The actual splitting of the incoming laser beam to enable coupling into multiple outgoing fibers occurs within a connector body. The body is typically adapted for screw engagement with each connector fitting to achieve appropriate alignment of each fiber end with the beam splitting apparatus within the connector body. Connectors exemplary of this type are manufactured by Dainichi-Nippon Cables, Ltd. of Tokyo, Japan. Such beam splitting connectors are not intended for nor adaptable to high power laser beam applications. Such connectors appear to rely on aligning of the fiber ends without any special conditioning of the laser beam split portions prior to their injection, for continued transmission, into the outgoing fibers. In the case where such a connector is being used to couple a high power laser beam, fiber misalignment will result in a stray portion of the beam impinging on a portion of the connector body, and/or a supporting ferrule, to cause heating. Such heating will at very least cause thermal distortion, if not physical damage, to the connector resulting in further misalignment. Additionally, as described in greater detail below and as known in the art, power laser beam injection into an optical fiber is most efficiently achieved where the beam is focussed onto the prepared fiber end in accordance with specific criteria. Thus, the mere alignment of fibers to achieve coupling therebetween is an extremely inefficient connection and one that is not feasible for the coupling of a high power laser beam.
The second major technique for coupling together multiple optical fibers consists of splicing techniques in which the multiple fibers being coupled are fused together. U.S. Pat. No. 4,263,495 to Fujita et al. discloses such a technique in which the fusing is achieved by irradiation of the multiple fibers with a CO.sub.2 laser. Other techniques for such fusion, e.g. by use of an electric arc, are also known in the art. Such splicing techniques result in average splice losses that are apparently acceptable for communication or low power applications. However, the inventors herein believe that based on the dB losses indicated for such splices, transmission of a power laser beam through the splice would result in heat generation and subsequent failure of the splice.
It is therefore a principal object of the present invention to provide apparatus for splitting a high power laser beam, delivered by an incoming optical fiber, into a plurality of split beam portions and coupling those portions into a like plurality of outgoing fibers for continued transmission therethrough.